Mono-bloc catadioptric (or “catadioptic”)lenses are known. One of the first was suggested by Dmitry Maksutov, who showed more than half a century ago that the two-separate-mirror system named after him can be made more rugged and stable by fabricating it in a glass mono-bloc. The design is shown in FIG. 1 and described on page 307 (FIG. 29a) of “Composition (Design) of Optical Systems” by M. M. Rusinov, Mashinostroenie, 1989, Leningrad, Russia. However, Maksutov encountered significant difficulties in actually fabricating his lens, which required centering four spherical surfaces and keeping a high tolerance of the central bloc thickness. Also, the saggitae of all surfaces had to be accounted for in the design and fabrication.
Mono-bloc catadioptric lenses were disclosed in a number of U.S. patents, including U.S. Pat. No. 5,793,538 to Cameron et al, and U.S. Pat. No. 5,042,928 to Richards. Cameron's solid catadioptric lens includes a substantially planar input surface, a primary concave mirror, a secondary convex mirror and a substantially spherical exit surface. The lens is composed of a solid material chosen according to the particular imaging application in which the lens is to be used. Radiation enters lens through the input surface, travels through the solid material and is reflected off the primary mirror. Radiation subsequently passes internally through the solid material and is reflected off the secondary mirror. Subsequent to being reflected off the secondary mirror, the radiation passes through the solid material and out of the lens through the spherical exit surface and onto a detector array for imaging purposes. In Cameron's lens, all surfaces are spherical (including the “planar” surface, which has a substantially infinite radius.
Richards discloses a single hybrid optical element that contains a reflective outer annulus zone and a refractive inner core zone to produce a single catadioptric lens element of high quality and high efficiency. The “hybrid” attribute indicates that the lens is composed actually of two distinct optical elements. Richards's system is basically a Bowen-type system, which has a first mirror smaller then a second one. It has six surfaces—four refractive and two reflective and produces two images, one from the central refractive lens the second from the mirror system. In a particular embodiment, the reflective outer annulus zone of the element utilizes Siedentopf's cardioid formulation and the refractive inner core zone utilizes the Cartesian formulation. A key requirement of this combination, for coherent applications, is the proper phasing of the two zones, which can readily be accomplished by tuning whichever zone is most convenient.
Non-imaging mono-bloc lenses with aspheric surfaces are known (e.g. in multi-focal lenses), but these surfaces are not surfaces of revolution. The use of aspheric surfaces yields well known advantages
It would be therefore advantageous to provide a mono-bloc Maksutov type catadioptric imaging lens with multiple on-axis aspheric surfaces, which can be designed in various materials for operation in the visible spectral range and/or the near and far infrared spectral range (spectral range of 0.4-15 micrometer).